1 Answer
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You can apply the method from http://tex.stackexchange.com/a/10365/15616 to the gap in DN. I tried also to use the same for EM, but curiously that deleted the whole line up to the intersection point as well. So there I just used a gap in the middle.

Explanation:

This uses the intercept calculation of xypics. Compare for example ⟨place⟩ of Figure 1 in XY-pic Reference and point 3j there. By using this in the context of an arrow (see Figure 14 ⟨labels⟩ and ⟨anchor⟩) this calculates the intersection point of the line given by {[l];[dr]}, relative to the current node, and the current arrow.